1. Field of the Invention
This invention relates to an outboard motor having an internal combustion engine including a valve operating characteristics variable mechanism that changes operating characteristics of intake valves and exhaust valves in response to the revolution speed of the engine.
2. Description of the Related Art
Also for engines of outboard motors, efforts have been made for higher outputs. For example, there is a trial of enhancing the air intake and exhaust efficiency to increase the output by providing a plurality of intake/exhaust valves in each cylinder (see Japanese Patent Laid-Open Publication No. hei 8-93585). There is also a valve operating characteristics variable mechanism brought into practice, which changes operating characteristics of intake/exhaust valves in response to the revolution speed range of the engine for the purpose of attaining higher output and lower fuel consumption of a vehicle engine. This valve operating characteristics variable mechanism is hydraulic, in which hydraulic pressure of its operating section is controlled by a hydraulic control valve.
Outboard engines are often driven continuously in different revolution speed ranges, such as in a trolling condition under a low revolution of the engine or in a cruising condition under a high revolution of the engine. However, conventional outboard motors are each monotonous in lifting amount and valve-opening period, which are operating characteristics of intake valves and exhaust valves, throughout the entire revolution ranges of the engine. Therefore, a lifting amount and a valve-opening period exhibiting high output characteristics in a specific revolution range, such as in a low revolution range (or high revolution range), might not be optimum in a revolution range different from that specific revolution range, such as in a high revolution range (or low revolution range), and this invites a decrease of the output or deterioration of fuel efficiency in the high revolution range (or low revolution range).
Toward higher output and higher fuel efficiency, it would be possible to employ the above-mentioned valve operating characteristics variable mechanism for vehicles. However, if it is used in an outboard motor whose compact engine is housed in a narrow space within an engine cover, simplification of oil paths and convenience for maintenance of control valves arise as new problems.
It is therefore a general object of the invention to provide an outboard motor capable of enhancing output energy and increasing the fuel efficiency by means of a hydraulic valve operating characteristics variable mechanism and also capable of simplifying oil paths and facilitating maintenance of hydraulic control valves.
A further object of the invention is to improve the accuracy of a bearing and facilitate maintenance of an oil filter.
A still further object of the invention is to facilitate assemblage of hydraulic control valves.
According to the invention, there is provided an outboard motor having an engine which includes an engine body mounted to a mount case with a mount wall portion of the engine body and defining a crank chamber containing a vertically extending crank shaft and bearing portions rotatably supporting the crank shaft, an intake valve and an exhaust valve for opening and closing an intake opening and an exhaust opening, respectively, which open to a combustion chamber, and a valve driving mechanism for opening and closing the intake valve and the exhaust valve, characterized in that:
at least one of the intake and exhaust valves being a plurality of such valves for each cylinder of the engine, the valve driving mechanism including an hydraulic-driven valve operating characteristics variable mechanism which changes operating characteristics of at least one of said intake and exhaust valves among the plurality of intake valves or exhaust valves in accordance with the revolution speed of the engine, an hydraulic oil path for supplying the valve operating characteristics variable mechanism with hydraulic oil being branched at a branching portion from a lubricant oil path for supplying the bearing portions and the valve driving mechanism with lubricant oil released from an oil pump driven by the engine, the branching portion being formed in a wall portion of the engine body other than the mount wall portion, and a hydraulic control valve for controlling pressure of hydraulic oil at the branching portion.
According to the invention summarized above, since at least one intake valve or exhaust valve among a plurality of intake valves or exhaust valves of each cylinder is changed in operating characteristics by the valve operating characteristics variable mechanism in accordance with the revolution speed of the engine, optimum operation characteristics can be set in different revolution ranges from the viewpoint of realizing higher output energy and lower fuel consumption. Additionally, since the hydraulic control valve is provided in the wall portion of the engine body other than the mount wall portion having a mount surface for engagement with the mount case, maintenance of the hydraulic control valve is possible without removing the engine.
Further, since the hydraulic control valve is located at the branching portion of the hydraulic oil path that branches from the lubricant oil path for supplying the bearing portion of the crank shaft and the valve driving mechanism with lubricant oil, length of the hydraulic oil path from the hydraulic control valve can be decreased. This results in elongating the portion of the oil path from the oil pump to the branching portion, which can be commonly used as the oil path of the lubricant oil for lubrication and as the oil path for hydraulic oil. Therefore, arrangement of the lubricant oil path and the hydraulic oil path can be simplified, and an increase of the cost caused by formation of the hydraulic oil path can be prevented.
An engine oil path forming a part of the lubricant oil path and an oil filter for lubricant oil flowing in the engine body oil path to pass through may be formed in the engine body. In this case, the branching portion is located in the lubricant oil path downstream of the oil filter.
In this arrangement, since the hydraulic oil is clean lubricant oil freed from foreign matters by the oil filter, foreign matters once entering into the lubricant oil do not intrude to the spool valve and the valve operating characteristics variable mechanism, and these components keep properly operative for a longer period, which also makes the maintenance easier.
The engine body may have a cylinder block and a crank case that partly define the crank chamber, the bearing portion may be made up of the cylinder block and a bearing cap, and the oil filter may be disposed in the crank case that forms the front wall portion of the engine body.
In this arrangement, since the use of the bearing cap makes it possible to precisely set the leakage of lubricant oil at the bearing portion, it contributes to improving the accuracy of the bearing and ensuring rigidity of the bearing portion more easily.
The cylinder block may have a deep skirt portion and the wall portion may be a cover that is fixed to the cylinder block to form a part of the upper wall portion of the engine body and permits the crank shaft projecting from the crank chamber to pass through. Additionally, a case oil path formed in the crank case among oil paths making up the engine body oil path may be connected to a block oil path formed in the cylinder block via a cover oil path formed in the cover.
In this arrangement, since the branching portion is formed in the cover that constitutes the upper wall portion of the engine body, maintenance of the hydraulic control valve is made easier. Additionally, when the hydraulic control valve is previously attached to the cover integrally, the hydraulic control valve and the cover can be prepared as a unit, and this facilitates assembly of the hydraulic control valve in the engine body.
In so far as used in this specification, the terms xe2x80x9cfront, back, left and rightxe2x80x9d indicate those of a ship body to which the outboard motor is mounted unless particularly indicated otherwise.